1. Field of Invention
The present invention relates to an inertia switch for sensing shock or vibrations imparted to an object to which the switch is secured, and wherein the switch consists essentially of a pair of spaced-apart, electrically-conductive contact plates, each having at least one cavity therein in opposed aligned relationship with a metal ball loosely captive between the pair of cavities and in contact therewith to establish an electrical conductive path through the ball, and wherein the ball engages each of the cavities at at least two contact points.
2. Description of Prior Art
Inertia switches having metal balls which are displaceable by shocks or vibrations to effectuate a switch function to inditate a disturbance are known. There are many known types of such switches and some of these utilize magnets or other means to retain the metal ball at a predetermined position. Once the ball is displaced the switch requires mechanical or electrical resetting. A major disadvantage of inertia switches is that many of these must be mounted in a precisely oriented manner in order to operate. Accordingly, such switches have found limited utility. A still further disadvantage of inertia switches which utilize balls is that often the electrical contact between the ball and the contact element is serious affected by the infiltration of dust particles or other foreign matter within the switch casing.
The improved inertia of the present invention is an improvement over the shock and vibration sensitive switch as disclosed in U.S. Pat. No. 4,467,153. In that patent there is described a switch construction in which two E-shaped electrodes are mounted in a frame member in planar alignment, one on opposite sides, and define dual cavities between the arms of the electrode. Two cylindrical conductive members are retained loosely captive between the two cavities formed between the E-shaped electrodes. The circumference of the cylindrical element is such as to contact two arms of the electrodes to establish a contact thereacross. Accordingly four contacts are established by the two conductive cylinders and the electrodes. A major disadvantage of this switch construction is that it can only operate effectively when positioned vertically along its longitudinal axis. Therefore, it can operate either right side up or up side down. If the housing is mounted at a slight angle from its axis, its sensitivity is minimized and may produce false switch closures and alarms. U.S. Pat. No. 4,185,180 also discloses an inertia switch which utilizes two plates having a through bore therein with an ondulated rim and a conductive rod element is captive between the aligned cavities or through bores. Such switch also has a disadvantage of having to be mounted at a precise orientation in order to work. This type of unit has a shorter period of discontinuity when vibrated.